FERTILITY 



FERTILIZATION 



1221 



in a hole about 1 inch in diameter and 2 feet deep at 

 each place where a tree is to be set. Such treatment 

 tends to promote filtration, to set free plant-food Ijy 

 aeration and to improve the physical condition of 

 the adjacent soil, while at the same time it lessens 

 the labor necessary to prepare the ground for tree- 

 setting. 



Barn manures, when properly cared for and intelli- 

 gently applied, not only furnish acceptable plant-food 

 but humus as well. Fertility and high productivity 

 usually may be maintained many years by means of 

 superior tillage, leguminous harvest and cover-cro])S, 

 and the manures of the farm. In some cases a high 

 state of fertility can be maintained only by occasional 

 applications of commercial mineral fertilizers, such as 

 phosphates and potash, but too often expensive ferti- 

 lizers have been substituted for tillage, leguminous 

 plants and bam manures. 



Fertility may frequently be promoted by light 

 applications (ten to twenty bushels to the acre) of 

 quicklime. Lime serves to make plant-food more 

 available, to improve soil texture and to correct aeitiity. 

 It may also be applied beneficially to a green-manure 

 fallow. Lime tends to sink into the soil, therefore 

 it should be applied after the last plowing preceding 

 the seeding, and should be covered and mixed with the 

 soil by tillage. Hydrated, or biting lime, not only tends 

 to Bet free plant-food but to flocculate the soil, thereby 

 improving its physical condition. Its use is especially 

 recommended on clay and moist lands and in orchards 

 where the ground is much shaded. Applications of 

 gypsum and salt are sometimes beneficial in main- 

 taining fertility, but they, as well as lime, usually act 

 indirectly, as the soil is seldom deficient in the.se con- 

 stitutents so far as they are required as plant-food. On 

 high-priced lands, especially those devoted to horti- 

 culture, the soil should be made and kept fertile — well 

 up to its highest productive power. 



A bare summer fallow of one to three plowings and 

 suitable surface tillage will not only destroy weeds, but 

 liberate plant-food as well, wliile storing moisture in 

 the soil for the immediate use of young plants. But a 

 bare fallow, if not accomjianied by the addition of some 

 plant-food, may hasten the depletion of the soil. It 

 is a matter of judgment, then, as to whether the particu- 

 lar soil contains such abimdant supplies of plant-food 

 that some of them may be removed; or whether it is 

 very deficient. In the latter case a green fallow would 

 be far preferable to a bare one. In many cases a bare 

 fallow is merely a method of mining-farming which 

 hastens the time when the land must be turned out 

 to pasture for economic reasons. Often productivity 

 is increased more satisfactorily by means of green- 

 manuring than by bringing plant-food to the land 

 from outside sources. In most of the humid districts 

 earlj' sowed peas (which withstand late frosts) followed 

 by buckwheat, and both plowed under some time 

 before they mature, can be grown in time to fit the 

 land for seeding in September to wheat, rye or timothy, 

 the nurse crop being omitted. When the land might 

 be made too porous by this method, rye sowed in the 

 fall, plowed under before coming to head and followed 

 by peas, would greatly improve the light and sandy 

 Boils by bringing stores of nitrogen and humus. 



Nature, in producing and storing fertility, provides 

 a great variety of plants and an infinite number of 

 ways of multiplying them so that the land is fully 

 covered with vegetation — except in desert regions. 

 Upon the best of these lands a vast animal life is main- 

 tained while the remainder produces other plants to 

 feed other animals. In the densely settled agricul- 

 tural districts of China, for the last two thousand 

 years the farmers have been returning as much to the 

 land as they have taken from it; and the soil is now 

 more productive than it was when first brought into 

 cultivation. The problem of conservation and resto- 



ration of soils is now in .Vmeriea the most serious one 

 tlie agriculturist has to solve. 



Sometimes soils are rendered unfruitful by the 

 presence of deleterious substances, as organic acids or 

 alkaline salts, or a superabundance of some one or 

 more of its usually useful ingredients, as water or 

 nitrogenous compounds. An excess of nitrogen stimu- 

 lates the growth of stalk and straw at the expense of 

 grain, or in the orchard it tends to the formation of 

 wood rather than to fruitfulness. The acidity should 

 be corrected by lime, as noted above, the surplus water 

 removed by drainage, the nitrogenous matter reduced 

 by the production of such crops as are not harmfully 

 affected by its superabundance, such as forage crops 

 which are prized for their foliage rather than for their 

 .seeds, while the alkalinity may sometimes be overcome 

 by deep tillage, irrigation or application of gypsum in 

 suitable amounts. j p^ Roberts. 



FERTILIZATION is the fusion of sexually differ- 

 entiated cells, and with special reference to the seed 

 plants it means that a cell (a fertilized egg, or zygote) 

 is thus formed which is capable of developing into the 

 embryonic plant later recognized in the plantlet of 

 the seed. The fusing cells, or gametes, are (1) the egg 

 (female cell), which is organized in the ovule, as 

 described below, and (2) a sperm-cell, or nucleus (male 

 cell), developed in the germi- 

 nating pollen-tube. Fertiliza- 

 tion is a process which may not 

 be readily observed in the seed- 

 plants except through the use 

 of careful histological methods, 

 both in the fixation of material 

 and in the subsequent pro- 

 cesses of imbedding and stain- 

 ing. The phenomena are illus- 

 trated in Figs. 149.5-1497. 



The term "fertilization" has 

 always implied the union of 

 male and female cells; but 

 formerly, when less was known 

 regarding the details of the 

 phenomenon, " fertilization " 

 included the mere mechanical 

 process whereby jjollen from 

 the anther was transferred by 

 any agent to the stigma of the 

 flower. For this reason "fer- 

 tilization by insects" or "fer- 

 tiUzation by wind" — meaning 

 the transfer of pollen by these 

 agencies — are frequent expres- 

 sions in the work of Darwin 

 In this last-mentioned sense, the word 

 pollination is appropriate, and now commonly em- 

 ployed. If the silks of corn are polhnated with corn 

 pollen, fertihzation normally ensues and seeds are 

 produced; but if the corn-silks are polhnated by the 

 pollen of the Uly, no seeds will be formed. It is obvious 

 that cross-pollination has no limits; but cross-fertihza- 

 tion is Umited to those cases in which the sexual cells 

 unite and a new organism develops. 



The development of some structures essential in 

 fertilization are of interest in this connection. The 

 mature pollen-grain consists of a large tube-cell and 

 nucleus and a small generative cell and nucleus. When 

 lodged upon a suitable stigma the pollen-grain germi- 

 nates by the development of a tube which enters the 

 loose tissue of the stigma and grows further into the 

 conducting parts of the style. In some cases, definite 

 stylar canals are present, but usually the tube wedges 

 itself between the yielding cells, absorbs nutrient in 

 its course, and forces or dissolves its way to the ovule 

 or seed-case, where, as a rule, it enters the micropyle 

 and approaches the embryo-sac and egg-cell. In its 



1495. A pollen-grain of 

 Lilium philadelphicum . 



Section of a single grain 

 before the anther opens; t, 

 the tube-cell; g, the genera- 

 tive cell. The large spheri- 

 cal body in each cell is the 

 nucleus. ( Magnified 500 

 diameters.) 



and Wallace. 



